Number 237, August 15, 1995 by Phillip F. Schewe and Ben Stein BOSE-EINSTEIN CONDENSATION (BEC) OF LITHIUM ATOMS has been demonstrated by physicists at Rice University (Randall Hulet, 713-527-6087). Like the condensation of rubidium atoms (reported last month, Update 233), the condensation of the much lighter lithium atoms begins with cooling to nanokelvin temperatures in an atom trap employing both laser beams and magnets. The Rice researchers believe that their gas of Li atoms passes over into the Bose- Einstein state---in which as many as 100,000 atoms coalesce into a single atomic state---at a temperature between 400 and 100 nK. They measure the temperature and density by passing a laser beam through the trapped atom cloud and recording the shadow cast by the atoms. BEC is detected by the diffraction of the probe light from the small (several microns in diameter) condensate. The formation of the Bose-Einstein state in Li atoms was somewhat of a surprise because it was thought that the very weak interaction (the so called van der Waals force) between atoms in the gas phase---attractive in the case of lithium, repulsive in the case of Rb---might cause the atoms to condense into a conventional liquid or solid rather than to the BEC state. The Rice scientists surmise that the zero-point energy of the Li atoms, the energy possessed the atoms at even the lowest of temperatures by virtue of the Heisenberg uncertainty principle, was able to overcome any van der Waals interaction, allowing the BEC state to form. (C.C. Bradley et al., 38 Aug. 95, Physical Review Letters. For science writers only: text and figures are available from AIP Public Information, physnews@aip.org) A MAJOR CLASS OF HEART ATTACK HAS UNEXPECTEDLY NON-RANDOM CHARACTERISTICS , new evidence suggests, opening the future possibility of clinical treatment with the tools of chaos theory. Always fatal within minutes, ventricular fibrillation (VF) is the uncoordinated twitching of muscle fibers in the main pumping chambers of the heart. Whereas most previous research has assumed VF to be a random process, an interdisciplinary team of researchers in Canada and the U.S. (including Daniel Kaplan of McGill University, danny@cnd.mcgill.ca) has found the first evidence for subtle patterns in the rhythms associated with VF. Analyzing the electrical activity during VF episodes in dogs, the team developed and applied statistical tests to demonstrate that the complex electrical rhythms of fibrillating hearts appear to have non-random "deterministic" characteristics; that is, they can be described by mathematical equations that relate the system's future state to its past and present conditions. Deterministic systems offer the possibility of "feedback control" of the type used to nudge seemingly random chaotic systems into a desired state. But the researchers caution that "the practical implementation of such control is still highly speculative and will present significant challenges." (F.X. Witkowski et al., Physical Review Letters, 7 August 1995.) In a separate development, Leon Glass of McGill University (514-398-4338) and Mark Josephson of Beth Israel Hospital in Boston (617-667-4387) have developed a mathematical model for describing a type of rapid heartbeat known as re-entrant tachycardia. Its further development may help cardiologists to better identify the condition and to learn the types of electrical activity in the heart that can trigger and terminate the condition. (L. Glass et al., upcoming article in Physical Review Letters. Texts and figures are available to science writers.) PHYSICS NEWS UPDATE will be in a summertime recess for three weeks.